browser: remove a dead unique_ptr constructor

this statement does nothing; remove it.

Bug: 1130379
Change-Id: I3eb01bfdef76b9613a17893a9651970eff736ad4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2420915
Commit-Queue: David Trainor <dtrainor@chromium.org>
Auto-Submit: George Burgess <gbiv@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Cr-Commit-Position: refs/heads/master@{#809222}

chrome/browser/updates/announcement_notification/announcement_notification_service_unittest.cc

@@ -107,7 +107,6 @@ class AnnouncementNotificationServiceTest : public testing::Test {
     TestingProfile::Builder builder;
     builder.SetPath(
         test_profile_manager_->profiles_dir().AppendASCII(kProfileId));
-    std::unique_ptr<sync_preferences::PrefServiceSyncable>();
     builder.SetPrefService(
         std::unique_ptr<sync_preferences::PrefServiceSyncable>());
     builder.SetProfileName(kProfileId);